For patients that lack the ability to produce antibodies, intravenous immunoglobulin replacement therapy, with immunoglobulin that is obtained from the plasma of blood donors, has proven a lifesaver. Over time, appreciation of the value of this medication for a number of different disorders has grown, increasing the demand. At the same time, awareness of the potential risk of viral contamination of the product has grown, leading to increasingly rigorous screening techniques that have coincidentally acted to reduce supply. The result is that this medication is often in short supply placing patients with Primary Immune Deficiency at great risk for life and well-being. Bayer Corporation, which manufactures the commercially available product Gamimune N. S/D, has responded to this challenge by developing a new purification process. The new formulation, Immune Globulin Intravenous (Human), Chromatography (abbreviated as IGIV-C) is a highly purified, liquid, intravenous immunoglobulin (IVIG) product. Its primary difference from currently marketed IVIG products is that a number of intermediate chromatographic steps are included in the purification of the product from human plasma. This chromatography-based process, while maintaining the initial ethanol precipitation steps, alleviates a number of labor intensive and time consuming intermediate centrifugation steps, substituting a more closed manufacturing system which reduces the risk of contamination, provides a more gentle treatment of the immune globulin proteins, and yields a final IgG product that is purer and more closely reflects the IgG subclass distribution found in plasma. The present study is a randomized, double-blind, parallel-group, multicenter, therapeutic equivalence trial of IGIV-C and the commercially available product Gamimune N. S/D that is intended to determine whether these two formulations are, in fact, therapeutically equivalent.